Aptitude - Boats and Streams - Discussion
Discussion Forum : Boats and Streams - General Questions (Q.No. 8)
8.
A boat takes 90 minutes less to travel 36 miles downstream than to travel the same distance upstream. If the speed of the boat in still water is 10 mph, the speed of the stream is:
Answer: Option
Explanation:
Let the speed of the stream x mph. Then,
Speed downstream = (10 + x) mph,
Speed upstream = (10 - x) mph.
 |
36 | - | 36 | = | 90 |
| (10 - x) | (10 + x) | 60 |
72x x 60 = 90 (100 - x2)
x2 + 48x - 100 = 0
(x+ 50)(x - 2) = 0
x = 2 mph.
Discussion:
85 comments Page 3 of 9.
Priya said:
6 years ago
x = 10.
36/(10-x) - 36/(10+x) = 90/60,
36/(10-x) - 36/(10-x) = 3/2.
then 12*4 = 36.
divide all no. * 12.
12/(10-x) - 12/(10-x) = 1/2.
(12/(x-y)- 12/(x+y)) / ((10-x)(10+x)) = 1/2.
Multiply by * 2 all equation.
24(10-x) - 24(10+x) = (10-x)(10+x),
240 + 24x - 240+ 24x = (10-x)(10+x),
24x + 24x = (10-x)(10+x),
48x = 100+10x-10x-x^2,
48x = 100- x^2,
48 = 100-x,
x= (100/48),
x = 2.
36/(10-x) - 36/(10+x) = 90/60,
36/(10-x) - 36/(10-x) = 3/2.
then 12*4 = 36.
divide all no. * 12.
12/(10-x) - 12/(10-x) = 1/2.
(12/(x-y)- 12/(x+y)) / ((10-x)(10+x)) = 1/2.
Multiply by * 2 all equation.
24(10-x) - 24(10+x) = (10-x)(10+x),
240 + 24x - 240+ 24x = (10-x)(10+x),
24x + 24x = (10-x)(10+x),
48x = 100+10x-10x-x^2,
48x = 100- x^2,
48 = 100-x,
x= (100/48),
x = 2.
(1)
Naveen said:
7 years ago
If we put x=2 in 36/(10-x)-36/(10+x) = 90/60,
We get 1=3/2.
Which is invalid, then how can we say that x= 2?
Anyone can tell me?
We get 1=3/2.
Which is invalid, then how can we say that x= 2?
Anyone can tell me?
Sarath.j said:
7 years ago
Please tell me the shortcut way to get the answer.
Anomii said:
7 years ago
I solved like this;
36/t =10+x.
36/t+1.3=10-x.I am not getting the answer. Please anyone help me.
36/t =10+x.
36/t+1.3=10-x.I am not getting the answer. Please anyone help me.
Aryan said:
7 years ago
Time taken by upstream is 90 minutes more then the time taken by downstream.
Revathi said:
7 years ago
Why are we subtracting downstream and upstream? Please explain.
(1)
Karthikeyan Vaithilingam said:
8 years ago
There can be 2 answer if we consider (x+50)(x-2) = 0.
x can be 2 or x can be -50.
I think speed cannot be in negative as only 2 is the valid answer.
x can be 2 or x can be -50.
I think speed cannot be in negative as only 2 is the valid answer.
Sriteja said:
8 years ago
Why have we done addition here instead of subtraction? Please explain.
Manjunath said:
8 years ago
Why had we done subtraction here? it means why won't we did addition? Please explain.
Diwakar said:
8 years ago
1 mile = 1600 meters = 1.6 km.
Post your comments here:
Quick links
Quantitative Aptitude
Verbal (English)
Reasoning
Programming
Interview
Placement Papers